Norovirus might be the perfect human pathogen. It hacks our DNA to create new noroviruses, gives us diarrhea, makes us puke so that the virus can spread to new hosts—and it spreads like wildfire. More than 1.1 million people in Britain have been infected so far this winter. According to the Centers for Disease Control and Prevention (CDC), norovirus causes 21 million illnesses annually in the United States. Approximately 70,000 require hospitalization and around 800 die each year.

Norovirus first appeared in Norwalk, Ohio, in November 1968, but how the virus gets into our cells still isn't well understood. "It’s not even clear exactly which type of cell they invade once they reach the gut," Carl Zimmer writes at National Geographic. “Regardless of the type, they clearly know how to exploit their hosts. Noroviruses come roaring out of the infected cells in vast numbers. And then they come roaring out of the body. Within a day of infection, noroviruses have rewired our digestive system so that stuff comes flying out from both ends.”

The viruses, says Zimmer, alter our intestinal lining and cause the cells to dump fluids, which contain many noroviruses (5 billion per gram of feces, in fact). And they make us repeatedly projectile vomit by tapping into our nervous systems and making our nerves send signals that will quickly contract the muscle lining of the stomach. Again, how these viruses do it is a mystery, but some studies have shown that during a norovirus infection, the digestion of food is slowed down. “In other words,” Zimmer says, “they seem to load up the stomach in preparation for vomiting.” Once outside the body, the viruses float through the air and end up on counters, food, and any other surface you can think of. On hard surfaces, they can survive 12 hours; on contaminated fabrics, 12 days. They also survive freezing, heating, and bleaching.

According to Zimmer, scientists don’t have a good way to study noroviruses, because they haven’t figured out how to rear them in human cells in a lab environment. But they can look at how the viruses spread—and that’s where Vomiting Larry comes in.

Larry is a humanoid robot that projectile vomits puke laced with a fluorescent marker. This allows scientists at the Health and Safety Laboratory in Derbyshire, England, to study how far particles of vomit travel, become aerosolized, spread, and infect others. “That’s important,” says Maggie Koerth-Baker at BoingBoing (where the above video comes from), “because it explains one of the ways that viruses spread by vomiting manage to end up in everyday things like, say, frozen raspberries. Aerosolized vomit isn't something you can spot. It doesn't clean up easily. And even just a drop of it can pass on plenty of viruses.”

Right now, scientists have Larry rigged up to study noroviruses, which Ian Goodfellow, a professor of virology at the department of pathology at Britain's University of Cambridge, told Reuters is “one of the most infectious viruses of man. It takes fewer than 20 virus particles to infect someone. So each droplet of vomit or gram of feces from an infected person can contain enough virus to infect more than 100,000 people." Using Larry, they've determined that aerosolized vomit can travel about 10 feet away from the puker.

So what’s the easiest way to stay healthy? Use common sense: Avoid anyone with the symptoms of the virus, wash your hands with warm, soapy water (Goodfellow suggests counting to 15), and dry your hands thoroughly.